The printing of latent images per se, for purposes of security or authentication, is known. For example, Canadian Patent No. 1,172,282 to Trevor Merry provides a security device comprising overlying line deflection patterns which produce different macroscopically viewable images when overlain at different positions by a finding screen. The latent image disclosed by the said Canadian patent is comprised of parallel lines, portions of which are deflected a predetermined distance in the area of the latent image to define the same. The lines are, of course, readily visible and do not themselves provide any additional security feature apart from the latent image. Thus, in order to increase the level of security provided by such a security device it was previously necessary to combine a separate security feature with the device, thereby adding printing or embossing steps to the overall process for producing the desired security document.